The Friday File: The highest mountain in the US is Denali at 20,320 feet. The next 22 tallest US mountains are also in Alaska. Outside Alaska, the tallest mountain is Mount Whitney in California at 14,494 feet. Of the 96 US mountains over 14,000 feet (fourteeners) all are in Alaska, California, Colorado, or Washington. The tallest mountain east of the Mississippi is Mount Mitchell in North Carolina at 6,684 feet.